Knowledge of past atmospheric pCO2 is important for evaluating the role of greenhouse gases in climate forcing. Ice core records show the tight correlation between climate change and pCO2, but records are limited to the past ~900 kyr. We present surface ocean pH and pCO2 data, reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles (0-140 and 300-420 kyr). The data co-vary strongly with the Vostok pCO2-record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives, allowing for quantitative estimation of atmospheric pCO2 beyond the reach of ice cores.

Continental ice volume effect on d18Oseawater and sea level was derived from Waelbroeck et al. (2002, doi:10.1016/S0277-3791(01)00101-9). Model 1 uses the deconvolution of foraminiferal d18O and Mg/Ca to yield local salinity, Model 2 uses the theoretical concentration of salt due to changing sea level. Ages are derived from correlation of the ODP 668B oxygen isotope stratigraphy with the Vostok gas age scale. Boron data are acceptable if >=3. Note that ages of samples 19-22 were estimated by extending the linear correlation between the Vostok gas age scale and the sedimentation rate in ODP 668B.

Supplement to: Hönisch, Bärbel; Hemming, N Gary (2005): Surface ocean pH response to variations in pCO2 through two full glacial cycles. Earth and Planetary Science Letters, 236(1-2), 305-314